This invention generally relates to routine subcutaneous hypodermic injections, specifically to the identification of the injection tissue, whether intramuscular, subcutaneous adipose or intravascular.
Pharmaceutical companies recommend the tissue of injection for various drugs that are given by hypodermic needle. The purpose is to optimize the intended bioavailability of the injected medication. For example, antibiotics are generally recommended to be injected intramuscularly to assure rapid and complete bioavailability. In other cases, drugs such as insulin are generally desired to be injected into adipose tissue to slow the bioavailability. It is important to avoid accidental insulin injections into the non-recommended tissue. This would inevitably result in variability in blood glucose control. Additionally, some drugs may be required to be injected intravascularly. Currently, there is no known method that reliably determines which tissue a drug is being administered to. To achieve this objective, it is necessary to devise a method for reliably sensing a transition of the needle tip between tissue types during insertion.
The consequences of not adhering to the recommended injection tissue can lead to adverse physiological effects. For example, abscesses, induration, persistent local pain, and hematoma have been extensively reported. The problem of missing the intended injection tissue has been reported to be more prevalent in pediatric patients.
Currently, intramuscular injections are performed by subjectively feeling the needle transition into muscle. Although there may be a definite transition that can be sensed by touch, it is likely that the transition will not be felt. This is particularly a problem with obese, pediatric and geriatric patients. Clearly, there is a need for a reliable device to sense the transition and eliminate subjectivity.
Another known method for determining the location of a fat-muscle interface is to use ultrasound. This method has been used for several years on livestock to determine the fat layer thickness on animals. Unfortunately, this method would be cumbersome to implement for the purpose of sensing a hypodermic needle transitioning into muscle. The reason is primarily the need to use a separate ultrasonic transducer to provide depth information. This information can then be translated to needle depth. Thus, it is an indirect method and consequently not desirable for this application.